Internal waves pump waters in and out of a deep coastal embayment of a large lake

Abstract

Large internal waves are a ubiquitous feature of many thermally stratified lakes, and result in oscillating baroclinic flows that pump water into and out of deep coastal embayments. In the long, narrow, and deep Kempenfelt Bay of Lake Simcoe, we show that stratification and circulation were coupled, so that movements of the thermocline can effectively flush the embayment much faster than hydraulic residence time from river input alone. Internal currents were driven by long‐period internal waves and resulted in large horizontal excursion lengths of several kilometers, which could drive exchange of embayment waters with the main basin. If the embayments are long, wide, and deep, Coriolis forces also deflect the internal wave to follow the coastline on the right‐hand side in the direction of travel as a Kelvin‐type wave, resulting in a net cyclonic circulation in the embayment. This residual counterclockwise flow further facilitated flushing of Kempenfelt Bay. For the summer of 2015, we estimate that forced and free internal wave dynamics alone resulted in a seasonally averaged flushing timescale as short as 17 ± 6 d for the surface mixed layer, and of 13.5 ± 5 d for the hypolimnetic waters of Kempenfelt Bay. Kempenfelt Bay is representative of many long, deep, and narrow embayments found in the Laurentian Great Lakes and arctic fjords. The exchange processes investigated here are relevant for determining the dynamics of water quality parameters used as indicators to evaluate lake health and fish habitat.

Mixing, stratification, and plankton under lake‐ice during winter in a large lake: Implications for spring dissolved oxygen levels

“…10a). This increase in conductivity corresponds to an increase of 1.22 × 10 7 kg of NaCl in Kempenfelt Bay, consistent with the salt input from Barrie over the winter as some of the salts are retained in groundwater and released in summer months (Oswald et al 2019;Flood et al 2020), suggesting that most of the annual input of salt into the lake likely flows into the bay from river input. After ice-off when the water column mixed, the average conductivity increased to approximately 480 μS cm −1 , 40 μS cm −1 higher than at the start of the winter (Fig.…”

“…A main source of salinity in Lake Simcoe is river inputs such as Lovers Creek (Winter et al 2011; Flood et al 2020) on the south side of Kempenfelt Bay (Fig. 2c).…”

“…In winter, inferred salt concentrations from conductivity measurements could provide a useful tracer for the pathways of water that carry urban road salt from the edge of the bay (Flood et al 2020). Changes in salinity within the water column could indicate how water from the edges of the bay circulate into the deeper waters.…”

Increases in Great Lake winds and extreme events facilitate interbasin coupling and reduce water quality in Lake Erie

“…This study shows an increasing trend in the extreme wind events and its potential impacts on the water quality (e.g., water temperature, dissolved oxygen and phosphorus) of a large lake with multiple basins. It is intriguing to suggest that the frequency of analogous wind-induced events may be increasing in other large lakes with multiple basins (e.g., basins of Lake Geneva 50 , Lake Michigan—Muskegon Lake Bay 52 , and Kempenfelt Bay of Lake Simcoe 54 ), lake-rivermouth (e.g., Lake Michigan—Pere Marquette River 55 ), or interconnected basins of reservoirs (e.g., Knewstubb and Natalkuz Lakes in Nechako Reservoir 51 ). Clearly this is a subject that warrants further study.…”

“…Interbasin exchange has been observed in lakes with multiple basins elsewhere (e.g., Lake Geneva 50 , Nechako Reservoir 51 ) as well as in the Great Lakes region (e.g., Muskegon Bay 52 , Green Bay 53 , Kempenfelt Bay 54 , Pere Marquette River 55 ) . In Lake Michigan, for example, high winds can lead to coastal upwelling into Muskegon Lake causing episodic hypoxia 52 .…”